Improved coverage in wireless communication systems such as Third Generation Partnership Project (3GPP™) LTE is sought after for various reasons. Coverage improvements may call for an increase in practical gain of various physical channels such as the PDCCH.
For example, a 3GPP™ work item entitled “Study on Provision of low-cost MTC UEs based on LTE,” RP-121441, September 2012, sets forth a requirement for a new ultra high coverage mode for LTE with +20 dB of coverage. This may require up to 9 dB of practical gain for the PDCCH, provided in a dynamic way. More gain may be possible at the cost of additional memory and processing at the user equipment (UE).
One method for providing additional gain on channels such as the PDCCH is to increase the aggregation level (AL), which corresponds to the number of resources allocated to a control message. The current maximum AL in LTE is 8 control channel elements (CCEs). Even if the AL is increased to 32 CCEs, it is expected that this would contribute only 6 dB of gain for the PDCCH. Aggregation beyond 32 CCEs is problematic since it leads to an exponential increase in blind decoding options for the UE. Additionally, for bandwidth-constrained systems high levels of aggregation may not be feasible. For example, in a typical deployment scenario with a 10 MHz system bandwidth, a sub-slot is only capable of accommodating 55 CCEs, so the next aggregation level of 64 CCEs is not feasible.
Another potential approach is to dynamically increase the power of the CCEs for UEs which are in limited coverage situations. However, this solution currently provides only about 5 dB of coverage gain before spatial re-use problems arise.
As described for example in Chapter 2 of “LTE—The UMTS Long Term Evolution: From Theory to Practice,” 2nd Edition, S. Sesia, I. Toufik, M. Baker, Wiley, 2011, the concept of blind HARQ combining has been proposed for broadcasted system information blocks sent on the physical downlink shared channel (PDSCH) of an LTE system. However, in this case the PDCCH is used to indicate the location of repeated data within a sliding window.
Therefore there is a need for a method and system for implementing HARQ on an LTE downlink control channel that is not subject to one or more limitations of the prior art.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present technology. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present technology.